In the following description, unless the context indicates otherwise, a reference to a “pixel” includes a reference to a picture element of a liquid crystal display and/or a reference to a region of the liquid crystal display corresponding to the picture element.
A liquid crystal display utilizes liquid crystal molecules to control light transmission in each pixel. The liquid crystal molecules are driven according to external video signals received by the liquid crystal display. A conventional liquid crystal display generally employs a selected one of a frame inversion system, a line inversion system, or a dot inversion system to drive the liquid crystal molecules. Each of these driving systems can protect the liquid crystal molecules from decay or damage.
A typical method relating to the dot inversion system is so-called 2-line inversion driving. FIG. 8 schematically illustrates a series of polarity patterns of part of a liquid crystal display using a conventional 2-line inversion driving method. In order to simplify the following explanation, only 4×4 pixels forming a sub-matrix are shown. Other pixels of the liquid crystal display have a polarity arrangement similar to the illustrated sub-matrix. As shown in FIG. 8, a polarity of each pixel in a first row is the same as a polarity of an adjacent pixel in a second row. A polarity of each pixel in a third row is the same as a polarity of an adjacent pixel in a fourth row, and is opposite to the polarity of the adjacent pixel in the second row. Polarities of the pixels in each column are opposite to the polarities of the adjacent pixels in each of the adjacent columns. Moreover, the polarity of each pixel is reversed once in every frame period.
By adopting the 2-line inversion driving method, the polarity of each pixel in a current frame is opposite to that in the previous frame and opposite to that in the next frame. Thereby, liquid crystal molecules in the liquid crystal display are protected from decay or damage.
However, when all the pixels are enabled and display video signals having the same gray level, a kind of brightness difference problem occurs between pixels in odd and even rows. Consider pixels A and B shown in FIG. 8 for example. Pixel A is in the third row and the first column, and pixel B is in the fourth row and the first column. FIG. 9 is a waveform diagram showing the waveforms of signals applied to pixels A and B. Scanning signals Vga and Vgb in the form of square waves are sequentially applied to pixels A and B in every frame period. An ideal waveform of the data signals applied to pixels A and B (shown as Vd1 in FIG. 8) should also be a square wave. However, due to interaction between the circuitries of the two corresponding adjacent pixels in the first column, signal distortion is liable to occur. As a result, the actual waveform of the data signals applied to pixels A and B is much like Vd2 as shown in FIG. 8.
In detail, in the (N−1)th frame period, pixel C in the second row and the first column has a positive polarity, and pixels A and B both have negative polarities. Because the video signals are applied to the pixels in a column sequentially, the positive polarity of pixel C may cause pixel A to be charged insufficiently, whereby the signal distortion is generated. This causes the brightness of pixel A to be less than that of pixel B. For the same reason, pixel A is not charged as sufficiently as pixel B in the Nth frame period and in the (N+1)th frame period. That is, the brightness of pixel A is always less than that of pixel B. Similarly, the brightness of the two pixels in the other pixel pairs like pixels A and B are always different from each other when a same gray level voltage is applied. Thus, the 2-line inversion driving method is liable to generate such differences in brightness between odd and even rows of the matrix of pixels of the liquid crystal display, and accordingly the display quality of the liquid crystal display may be unsatisfactory.
It is, therefore, desired to provide a method for driving a liquid crystal display which can overcome the above-described deficiencies.